Page:The New International Encyclopædia 1st ed. v. 13.djvu/773

* MOLTING. 695 MOLTING. ri-iiowiil is confined to "a sprinkling of new feathers here and there." Young Ijirds may also mult several times before they even acquire the feathers of adult structure, and many species need to pass through at least two molts besides those of the first summer before the plumage be- comes wholly of the pattern and color of the adult. The loss of feathers during the molting process is so compensated for by the renewal of feathers that few birds (the Anatida- and Konie other groups excepted) lose either the ability to fly or the protection afl'orded by their plumage. The feather areas are systematically replaced, tlie remiges falling out one after another in definite sequence and almost synchronously from each wing. The greater coverts are regularly re- placed before the fall of the .secondaries beneath them, the lesser coverts before the median, while even in the rows of the lesser coverts an alterna- tion appears to be attempted. On the body the protective sequence is less obvious, but the molt regularly begins at fairly definite jjoints. The month of August marks the maxinuim of the molting season, though there is more or less shedding of feathers in nearly every month of the year. A complete molt is accomplished in from fdur to six weeks, while partial molts rei|Uirc' nuich less time. A resemblance to the shedding of the skin of reptiles is seen in the ccdysis of the scaly feathers of the penguin, which peel off in flakes. In certain species of European grouse the claws, which grow to an inordiiujte length in winter, may be partly shed or worn off as spring advances ; the white pelican, both sexes of which during the breeding season bear on the ridge of the bill a horny projection, sheds it, so that these excrescences may be 'gathered by the bushel.' The puffin (q.v. ) and some of its allies molt even the horny sheath of the bill, together ^ith the outgrowths over the eyes. Sheddixg of Horn.s, etc., bv M.MMAI.S. In mammals the periodic shedding of the hair or pelage is comparable with molting; as is also the process of annually shedding the antlers, the new antler being larger and consisting of a larger number of branches or tines. In the deer family the horns of the male are deciduous toward spring, while the pronghorn drops its horns in the autumn. ilOLTING, OR ECDYSIS IN THE LoWEU CLASSES. In animals like Crustacea, Myriapoda, insects, and spiders, with a more or less solid exoskele- ton. too dense to permit of gradual growth or in- crease in volume, there must be a periodical cast- ing of the skin, or ecdysis. The same occurs in ~nlamanders. and especially in the scaly reptiles, In the Crustacea, insects, and similar animals the old skin dies and the new integument is formed by a secretion thrown out by the inner layer of epithelial cells called the liypoderniis. On removing the shell of the lobster the liypo- derniis is seen to be a richly colored reddish soft layer. The formation of the new layer of chitin arrests the supply of nourishment to the old skin, so that it dries and hardens, and is finally shuffled off. In the crayfish and presumably in the lobster (q.v.), as well as in lizards and snakes, the casting of the old skin is materially induced and aided by the growth on the surface of the hypodermis of a layer of very fine and equally distributed hairs, called 'easting hairs,' which, by their rigidity and position, mechanic- ally loosen and raise the old skin. These re- main as vestiges, forming spikes, ridges, or warts, serving to ornament the crust of crabs, or the outer edges of the skin-scales of snakes and lizards. In insects, where easting hairs are exceptional, the loosening and casting of the skin is brought about by the secretion of a fluid by the cells of the hypodermis. This fluid spreads over the whole surface when the cells are still soft and not hardened by exposure to the air. This same fluid, when the pupa extricates itself from the larval skin, extends around the whole pupa and serves to protect it and to glue together the wings, legs, antennfc, etc., in their new position. The process of molting as seen in caterpillars (e.g. Telea Pohjjihcinus) is thus. It changes its skin five times before changing to a chrysalis ; and the ecdysis occurs at regular periods, i.e. about every ten days for the first four mollings, while about twenty days elapse between the fourth and fifth casting. The operation usually takes place after 4 p.m. A little before this time it holds its body erect, grasping a leaf with the two pairs of hind legs only: the skin is wrinkled and detached from the body by the fluid previously mentioned; the body now energetically contracts, .so that the skin is pulled off and pushed toward the end of the body; the skin thus becomes so stretched that it soon tears just under the neck, and then .separates from the head. When this is accom- plished the most difficult operation is over, and now the process of casting goes on very rapidly. By repeated contractions the skin is folded to- ward the tail, like a glove when taken off, and the lining of the spiracles, mouth, fore st(miacU, and rectum conies out in long filaments. When about one-half of tlie body apjiears, the shell still remains like a cap, inclosing the jaws ; then the worm, says Trouvelot, as if reminded of this loose skull-cap. removes it by rubbing it on a leaf; this done, the worm finally crawls out of its skin, which is attached to the fastening made for the purpose. Directly after the ecdysis the larva increases in size, the head being distinctly larger as well as the body, which soon fills out. The lobster frequently molts after maturity. But in insects which undergo a ctmiplete meta- morphosis and which have the longest lives the number of molts is greatest. When the number is excessive this seems to be 4ue to some physical cause, such as lack of food combined with low temperature. In caterpillars the number of ecdyses appears to be (hqiendcnt on climate. Bibliography. For birds, consult : .J. Dwight, Jr., "The Sequence of Plumage and Molts of the Passerine Birds," in Aiimiln of the Ncio York Ararlcmij of Sciences, vol. xiii.. part I. (New Yoi-k, I'JOO), with a full bibliography as regards passerine birds; Xewton (with Gadow), Dicfion- ary of Birds (London. ISn.S-nfi) ; also the au- thorities mentioned under Cagk-Birus. For mammals: Beddard, Mammnlia (London, 1!)0'2); Caton. Antelope and Deer of America (Xew York. 1877). For rejitiles and Amphibia, authorities men- tioned under AMPHIBIA ; Snake. For insects, etc.: Semjicr. Animal Life as Af- fected hii the Xatiirnl Conditions of Existence (New Y^ork, 1881 ) ; Packard, Text-hook of Ento- mology (New York, 1898) ; Max Braun, Vcber
 * is snakes and lizards.